Fluid pressure operated circuit breaker



Jan. 13, 1948.

J. M. CUMMING 2,434,549

FLUID PRESSURE OPERATED CIRCUIT BREAKER Filed April 21, 1945 45 lam ngm' r "j 1' 5 :1 0 Z0 Q 1/ L w WITNESSES:

Patented Jan. 13, 1948 FLUID PRESSURE OPERATED CIRCUIT BREAKER James M. Cumming, Turtle Creek, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application April 21, 1945, Serial No. 589,581

Claims. (Cl. 200-82) This invention relates to fiuid pressure operative circuit breakers and, more particular, to control valve means for controlling the operation of such a circuit breaker.

Fluid pressure operative circuit breaker equipments designed for use in controlling high tension power circuits generally involve heavy movable parts which must be adapted for rapid operation. Compressed air at a pressure of approximately 150 to 350 pounds per square inch is frequently employed as the power medium for actuating circuit breakers of this type. Such a circuit breaker mechanism must be, for certain classes of Gil-cycle service, capable of effecting an open-close-open operation within a time interval of 17 cycles. Because of the power and speed of operation required for such a circuit breaker, it is desirable to provide a mechanism having maximum simplicity and ruggedness of design.

In a circuit breaker of the class embodying a spring for opening the contact elements and a piston subject to compressed air for closing the contact elements, in order to prevent excessive shock to the circuit breaker mechanism during operation of the actuating piston, it has been proposed to provide control valve means functioning to restrict or reduce the rate of the supply of compressed air to the piston cylinder during initial movement of the piston. This control valve means is designed to move quickly from a throttling position to an open position, to permit quick final build-up in pressure, following a predetermined initial movement of the piston, and preferably at the point in its traverse corresponding to the initial touching of the contact elements of the circuit breaker. In this way, the position is prevented from acquiring such a velocity as might result in damaging shocks during operation of the circuit breaker, while full operating force becomes available for overcoming any resistance to final closing of the breaker. Control valve mechanisms heretofore provided have proved successful in service, but occasionally difliculty has been experienced in insuring positive operation of such a control valve without variation in operating speed resulting from friction.

It is, accordingly, an object of my invention to provide an improved control or throttle valve mechanism for a fluid pressure actuated circuit breaker in which rugged and simple features of construction are combined to promote positive operation and to minimize the effect of friction on the speed of operation of the mechanism.

It is another object of the invention to provide an improved throttle valve mechanism of the above type which may readily be installed or built into a circuit breaker equipment of existing design without requirement of extensive alterations.

Other objects and advantages of the invention will appear in the following more detailed description thereof, taken in connection with the accompanying drawing, in which:

Figure 1 is a diagrammatic view, partly in section, of the operating portions of a fluid pressure operated circuit breaker equipment having associated therewith a preferred form of control valve mechanism constructed in accordance with the invention;

Fig. 2. is a fragmentary sectional view of the control valve mechanism shown in a closed position corresponding to the open position of the circuit breaker;

Fig. 3 is a sectional view taken substantially along the line IIIIII of Fig. 1; and

Fig. 4 is an enlarged detail fragmentary view of the operating lever of the control valve mechanism shown in Fig. 1.

Referring to the drawing, in Fig. 1 there is illustrated in diagrammatic form a portion of a single pole unit of a fluid-pressure-operated circuit breaker, comprising a suitable frame structure (not shown) supporting stationary contact elements 5 in the power circuit to be controlled, a movable resilient contact element 6 cooperative therewith and secured to a rod 1, a cylinder [0 having mounted therein an operating piston H, and a piston rod I2, the upper end l3 Of which is pivotally connected to the rod 7 through the medium of a beam l4 fulcrumed on a stationary pin ii. A coil spring I! is mounted in cooperative relationship with the movable contact element 6 for urging that element toward an open circuit position. The piston H is responsive to the pressure of air admitted to a pressure chamber 20 for actuating the piston rod I2, beam l4 and rod 7 to move the contact element 6 into circuit closing engagement with the stationary contact elements 5, in opposition to the force exerted by opening spring I? and contact spring 6.

For maintaining the circuit breaker elements just described in circuit closing position, the circuit breaker apparatus is further provided with a transversely disposed beam 22, one end. of which is journaled on a pin 23 carried by a link 24 that is in turn pivotally connected to a pin 2'5 carried by the frame structure. The beam 22 is peratively connected by means of a pin 28 to the piston rod H2 at a point above the cylinder iii,

and also carries, at the end opposite the pin 23, a

roller 39 which is adapted to be engaged by a suitable latch mechanism, generally indicated as 3!, for holding the beam 22 and the associated elements of the circuit breaker in the circuit closing position, as shown in Fig. l.

The latch mechanism 3| may be of any suitable design and, as illustrated, comprises a main latch member 32 journaled on a stationary pin 33 secured to the frame structure, a release pawl 34 pivotally connected to the frame structure by means of a pin 35 for cooperation with the latch member 32, and an auxiliary latch member 36' adapted for cooperation with the pawl 34. The main latch member 32' has a surface 38 adapted for latching engagement with the roller 30, and an extension lJ adapted for interlocking engagement with a portion of the pawl 34 for a resisting clockwise movement of the main latch member about pin 33 under the force tending to raise the end of the beam 22 carrying the roller, and thus tending to eifect disengagement of the latch member 32 from the roller. For biasing the main latch member 32 in a counterclockwise direction, there is provided a spring 32, which is interposed between a suitable lug on the frame structure and the head of a link pivoted to the latch member.

For tripping the latch mechanism 3|, there is provided a trip coil 44, which is adapted to be energized through the medium of a suitable trip control circuit (not shown) for causing upward movement of an armature carrying a plunger 45 that is operatively aligned with a portion of the pawl 34. The pawl 34 is normally urged into the position shown in Fig. 1 by means of a spring 41, which is adapted to yield upon operation of the pawl by the'trip plunger 45. The auxiliary latch member 35 is inoperative when the parts are positioned as shown in Fig. 1, but serves to hold the pawl 34 out of interfering engagement with latch member'S'A' when the beam'22 and otheroperating elements of the circuit breaker are in circuit opening position. A coil spring 49'is interposed between a portion of the cylinder structure II and a lug ilon the auxiliary latch 36, and acts to tilt the latter in a clockwise direction about pin 35; causing the lug 53 to carry the pawl 34 in the same direction, when the end of the beam 22 carrying roller 38 is swung upwardly during a circuit breaker opening operation, It will be noted that a lug 5! carried on the upper end of auxiliary latch Stis adapted-to be engaged by the free end of the beam 22, when that beam is moved to the circuit closing position as shown in Fig. 1. With the auxiliary latch member 35 thus held down, the spring 1! is permitted to maintain the pawl 34 in interlocking engagement with the main latch member 32.

For controlling the supply of fluid under pressure to the chamber 2!], there isprovided a ma net valve assembly, generally indicated at 55, comprising a casing having a valve chamber 55 communicating with a fluid supply pipe 51, which may be connected to any'suitable source of fluid under pressure. Within chamber 56 is mounted an inlet valve 58 for controlling communication from the valve chamber to a passageway 60 leading to the pressure chamber 20. The supply valve 5'! is normally urged toward a seated position by a coil spring 62 mounted in the valve chamber 56, and is provided with a valve stem 63 which extends upwardly and terminates in an armature portion (not shown) movably disposed within a magnet coil 65 carried by the frame structure. The magnet coil 65 is adapted to be energized through the medium of: a suitable control circuit (not shown) which may be arranged in any approved and well known manner for insuring the desired automatic operation of the circuit breakor equipment. The valve stem 63 also carries a discharge valve element 51 which is operative to vent the passageway 69 to atmosphere when the supply valve element 58 is in its seated position, as shown in Fig- I. Upon energization of the magnet coil 55, the stem 83 is shifted downwardly'to'close the valve element 61 while opening the supply valve 58 to effect supply of fluid under pressure to the pressure chamber 20 above the piston II,

It is not deemed necessary to illustrate the control circuits for the magnet coils 44 and 65, but it will be understood that any suitable circuit breaker controlling system may be provided to furnish the usual features of automatic operation well known in the circuit breaker art. For example, the trip'coil 44 maybe arranged for energizationin response to development of a fault in the main circuit controlled by the circuit breaker, or alternatively to be subject to manual control. If the circuit breaker equipment in eludes means for effecting a quick reclosing operation following an opening operation in response to a fault, the circuit for energizing the" magnet coil 65 may be arranged to initiate energization thereof instantaneously upon tripping" of the circuit breaker apparatus, to thus insure a subsequent reclosing operation with minimum loss of time.

According to the invention, a throttle valve asembly, indicated generally by the reference character 10; is provided for controlling the rate of supply of fluid under pressure through the passageway 69 to the piston chamber 20 at a rate determined in accordance with the operation of the circuit breaker. The throttle valve assembly includes a casing section H interposed between the magnet valve assembly 55 and the cylinder l0, and having a suitable bore 13 disposed substantially vertically and in intersecting relation with respect to the passageway 60, which,

casing section H, as isbest shown in Fig. 3. for

permitting flow of fluid around the bore 13 at a rate determined by adjustment of a screwthreaded valve element 15. Slidably mounted in the vertical bore 13 is a valve element 18. which is urged upwardly under the force of a coil spring- 19 that is interposed between the lower end of the valve e ement and a cap carried by the casing section H. in its uppermost position, as shown in Fig. 1, a channeled portion 8| thereof is disposed in registration with the passageway 60 so that flow of fiuid'under pressure is virtually unrestricted. On the other hand. when the valve element 18 is shif edto its lowermost position. as is best shown in Fig. 2, flow'of fluid under pressure through the" With the valve element 18 held passageway is limited to the flowarcael -thev bypass 14-.

The throttle valve element 18 is arranged foroperation in accordance with operation of the piston rod l2and associated elements of the cir-. cult breaker. For this purpose, a linkage mechanism is provided for operatively connecting the valve element 18- to the piston rod I2, comprising a main lever 03 which is pivotally mounted intermediate its ends on a pin 9| carried by a pairof lugs 92 projecting from the cylinder casing I0. One end of the main lever 90 is pivotally-connected by means of a pin 94' to an upper extension of the valve element 18, and the opposite end;

of the lever is providedwith aslot 96' (see Fig. 4) through which extends a, pin 9-! that is carried on the lower end of a substantially vertically disposed link member 98. The link member 98has anelongated slot as for receiving the outer end of the pin 28 carried by the piston rod I2, thus constituting a lost motion connection between thepiston rod and the lever 90. Also fulcrumedon the pin M is an operating lever I00 which is shorter in length than the main lever 90 and has one endconnectedto the pin 91*. The other end of the operating lever H30- is pivotally connected bymeans of a pin I0 I to an element I02, the outer end of which is connected by means of a pin I03 to a link i0 1 which is, in turn, operatively connected to pin I05 on the extreme end orthem-ain lever, outwardly ofpin 94. Suitable rollers may preferably be mounted on the pins I05 and I03. It will be noted that in, the normal position of the levers I00 and 90 the pins 91, I01 and I03 are not in alignment, and that if the operatinglever I00 is tilted counterclockwise about the pin 9!, relative to lever 00, the roller carried by pin I03 will be advanced outwardly, or to the right as viewed in Fig. 1.

A spring -pressed latch member IIil is pivotally mounted on the casing section 'II in operative alignment with the rollers carried by pins I05 and I03. As is best shown in Fig. 2 of the drawing, when the levers 90 and I00 are moved to aposition corresponding to the circuit opening position of the circuit breaker, the roller on pin I05 is disposed-in interlocking engagement with the latch member H0 while the. other roller on pin I03,

lightly engages the upper surface of' the latch member. It will thus be apparent that upon relativemovement of the operating lever I00 with respect to main lever 90', the roller on pin I03 willv be moved outwardly to release the latch member H0 from the roller carried by pin I05, thus permitting spring 80 to shift the Valve element 18 to its uppermost position. It should be noted, that the, latch IIO positively latches the throttle valve in its restricting position, independently of frictional forces, and is positively released by the linkage I00--| 02 prior to any movement of the valve element 18.

In. operation, if the. circuit breakerequipment is disposed in itscircuit closing position, as shown in, Fig. 1, the pin 28 carried by piston rod I2 is held in engagement with the lower end of the slot in, link member 08 and thus holds the associated levers 90 and I00 in such a position as tov maintain the throttle valve element 18 in its full open position, and free of any cooperation with the. latch member H0. At the same time the beam 22 is disposed in a substantially horizontal position with the roller Sit in latching engagement with the mainlatch member 32, so thatthe circuit breaker is positively held in the circuitclosing positionagainst. the force tending to open: the contact elements.

cuit,

movedupwardly, about the pin 23, while rod I2,

. beam I4, androd'l' are at the; same time actuated by the spring I to effect disengagement Qf'thecontact element fi from the elements 5.

The piston II is carried upwardly during the upward movement of the piston rod I2, but if the circuit breaker isequipped for a quick reclosing: operation, the operation of the usual auxiliaryreclosing means (notshown) results in energization of the magnet coil 65- in time to operate the supply valve 5.8:.for admitting fluid under pressuretothe piston chamber 20 before piston II has;

reached its uppermost position. Upon the resultant supply of fluid under pressure to chamber 20, the upward motion of the piston II will be reversed prior to any engagement between pin 28 and theupper end of the slotted link 98, so

that the throttle-valve 18 remains in its full openposition. Unrestricted flow of fluid under pres-- sure: through passageway 60 to piston chamber 20 is thus insured for supplying the added force needed for reversingthe movement of the mechanism and causing quick reclosure of the circuit breaker.

If the fault in the controlled circuit hasnot been removed at the time when the reclosure of the circuit breaker occurs, however, the trip coil rawl-11 again beenergized and coil 65 will be deenergized for venting the piston chamber 20' to atmosphere, thereby rendering spring I! again operative to: open the circuit breaker. It will be understood that suitable dump valve means may be provided for augmenting the discharge of fluid under pressure from piston chamber 20 in order topromotequick upward movement of" the piston IIi. Oneform of such dump valve anda suitable control circuit for the complete mechanism is shown in my Patent No. 2,361,178, issued October 24, 1944. For the purpose of discussing the present invention, however, it isnot deemed;

necessary to show such a dump valve and control circuit.

Assuming that the circuit breaker is moved to its-circuit opening position, with the contact element Sheld out of engagement with contact elements 5 under the force exerted by spring I1, it will be apparent that the beam 22 will be dis posed inthe position shown in Fig. 2 of the drawing. At the sametime, the operating piston I I will be in its uppermost position within cylin der II, while the pin'28 carried by the piston rod' t2 will be disposed at the upper end of the slot 99' of the link 98'. With the link 98 thus main tained in the position shown in Fig. 2, the valve" elementlB' will be latched in its lower or closed position, as shown, so that the communicationthrough passageway 60 is limitedto the bypass;

If the controlling circuit for the circuit breaker is now energized in theusual manner to causea closing operation, the consequent energiz ation' of the magnet coil Eli of magnet valvedevice 55* effects unseating of the supply valve element 58 against the force of spring 62, while discharge valve Bl is moved to seated position. Fluid under pressure is then supplied from the usual source by way of pipe 51, valve chamber 56, past the unseated valve element 58, and through passageway 6t and restricted bypass 14 to the piston chamber 29. The piston II is thereby moved downwardly for operating the rod I2, beam I4 and rod '5 to bring the movable contact element 6 toward the contact elements 5. It will b understood that although suflicient fluid under pressure is quickly supplied by way of the communications just described, including the restricted bypass i i, to effect prompt closing movement of the various circuit breaker elements, the increase in pressure of fluid in chamber 20 is nevertheless so controlled as to prevent the piston l I and the movable elements from acquiring an excessive velocity during the initial operation. As the piston ll continues its downward movement, the pin 28 carried by piston rod I 2 approaches the lower end of slot 99 in link 98 and at a predetermined point in the stroke of the piston l I, the pin 28 forces the link 98 downwardly. As hereinbefore mentioned, the exact point at which the pin 28 moves the link 98 downwardly during a circuit breaker closing operation, may be determined as desired by proper adjustment of the link 98, it being noted that this member comprises two screw-threaded parts which may be locked together by means of a set nut I20.

Upon initial downward movement of the link 98 and pin 9! carried thereby, the operating lever Hill is tilted in a counterclockwise direction about pin 9?, the main lever 90 remaining stationary whil pin 9? moves in the slot 96. This relative movement of operating lever I results in operation of the link H32 and roller I03 to force outwardl the spring-pressed latch element 1 I0, thus releasing the pin I85 and lever 90 to permit quick upward movement of the throttle valve element 78 under the force exerted by spring 19. The valve element 18 thus assumes its open position substantially instantaneously to continue the supply of fluid under pressure to the piston chamber 28 at an increased rate of flow by way of the channeled portion SI of the valve element, which is now in registration with the passageway Sil, as shown in Fig. 1. Pressure of fluid in chamber 26 is thus increased quickly by the supply of fluid under pressure at the maximum rate so that sufiicient force is exerted on the piston II to move it to its full circuit breaker closing position, regardless of the increase in resistance to such movement that may be caused during final closing operation of the contact elements 6 and 5.

It will be understood that the control valve mechanism iii is thus tripped in time to effect movement of the valve element 18 to its open position, as shown in Fig. 1, just prior to the possible reopening operation of the circuit breaker that may be initiated in case the circuit breaker is closed on a fault. Consequently, the control valve mechanism Ill will remain in th open position during a subsequent automatic reopening operation of the circuit breaker, as already explalned, to render instantly available the full pressure required to insure such reclosing operation in a minimum interval of time.

- From the foregoing description, it will be seen that an auxiliary control valve mechanism constructed in accordance with the invention may be embodied in any type of fluid pressure operated circuit breaker to afford adequate protection to the operating portions of the equipment during rapid movement under the high fluid pressures required. My improved control valve mechanism is simple in construction and comprises relatively few sturdy operating elements which are adapted to respond smoothly and substantially without variation in speed, due to friction or other cause, throughout a long service life.

Having now described my invention, what I claim as new and desire to secure by Letters Patent is:

1. In a fluid pressure operated circuit breaker having relatively movable contact means, 3, cylinder, a piston operative upon an increase in fluid pressure in said cylinder for moving said contact means to a circuit closed position, and means for moving said contact means to an open circuit position, the combination of supply valve means operative to supply fluid under pressure through a communication to said cylinder, throttle valve means interposed in said communication having a position for restricting flow therethrough and an open position for permitting maximum flow, means for biasing said throttle valve means toward open position, and a positive latch for releasably holding said throttle valve means in the restrictin position, and a member movable independently of the throttle valve means for releasing said latch during movement of said piston to permit said biasing means to move said throttle valve means to open position.

2. In a fluid pressure operated circuit breaker having relatively movable contact means, a cylinder, and a piston operative upon an increase in fluid pressure in said cylinder for moving said contact means, the combination of supply valve means operative to supply fluid under pressure through a communication to said cylinder, throttle valve means interposed in said communication having a position for restricting flow therethrough and an open position for permitting maximum flow, means for biasing said throttle valve means toward one position, a positive latch for holding said throttle valve means in the other position, and a latch release member operative upon predetermined movement of said contact means for releasing said latch to permit said biasing means to move said throttle valve means toward said one position.

3. In a fluid pressure operated circuit breaker having relatively movable contact means, operating mechanism including a cylinder, a piston operative upon an increase in fluid pressure in said cylinder for moving said contact means to a circuit closed position, and means for moving said contact means to an open circuit position, the combination of supply valve means operative to supply fluid under pressure through a communication to said cylinder, throttle valve means interposed in said communication having a position for restricting flow therethrough and an open position for permitting maximum flow, means for biasing said throttle valve means toward open position, a latch element for releasably holding said throttle valve means in the restricting position, and one or more links engageable with said latch element and connected to a movable part of the operating mechanism for moving said latch to unlatched position upon predetermined movement of said contact means toward the closed circuit position.

4. A fluid pressure operated circuit breaker having contact means movable to open circuit position and to closed circuit position, an operating 9 cylinder, a piston operative upon supply of fluid under pressure to said cylinder for moving said a contact means, fluid pressure control means including a passage for supplying fluid under pressure to said cylinder, valve means biased toward one position and movable to another position to control the rate of flow of fluid under pressure through said passage, a latch releasably operative to hold said valve means against the bias thereon, a link movable in response to movement of said contact means for shifting said valve means against its bias, and a second link also movable in response to movement of said contact means but movable prior to movement of the first said link for releasing said latch means.

5. A fluid pressure operated circuit breaker having contact means movable to open circuit position and to closed circuit position, an operating cylinder, a piston operating upon supply of flu d under pressure to said cylinder for moving said contact means, fluid pressure control means including a passage for supplying fluid under pressure to said cvl nder, valve means biased toward an o en position and movable to a throttling position to control the flow of fluid under pressure through said passage. a latch operative to hold said valve means in throttling position, a link having a lost motion connection with said p ston for shifting sa d valve means to throttling position so as to reduce the rate of su ply of fluid under pressure to said cylinder during initial movement of said contact means from the o en circuit position. and a second link having a lost-motion connection with the first said l nk and o erative to relea e said latch after sa d piston has been moved through a predetermined portion of a stroke.

6. A fluid pressure opera ed c rcuit breaker having con act means mo able to open circuit position and to cl sed circuit osition, an o eratln cylinder. a piston operative unon supply of fluid under pressure to sa d cylinder for moving said contact means to closed circuit position, sprin s means operative to move s id contact means to open c rcuit position. fluid pressure control means including a massa e for su plying fluid under pressure to said cylinder, valve means biased toward an open position and movable to a throttling position to control the flow of fluid under pressure through said passage, a latch releasably operative to hold said valve means in throttling position. a link connected through a lost-motion connection with said piston for shifting said valve means to throttling position so as to reduce the rate of supply of fluid under pressure to said cylinder during initial movement of said contact means from the open circuit position, and a second link having a lost-motion connection with the first said link and o erative to release said latch after said piston has been moved through a predetermined portion of a stroke in closing said contact means, said lever means being inoperative to move said valve means out of open position during a partial stroke of said piston in effecting a quick reclosing operation of said contact means.

7. A fluid pressure operated circuit breaker having contact means movable to open circuit position and to closed circuit position, an operating cylinder, 2. piston operative upon supply of fluid under pressure to said cylinder for moving said contact means to closed circuit position, spring means operative to move said contact means to open circuit position, fluid pressure control means including a passage for supplying fluid under pressure to said cylinder, valve means biased toward an open position and movable to a throttling position to control the flow of fluid under pressure through said passage, a positive latch operative to hold said valve means in throttling position, lever means cooperative with said piston for shifting said valve means to throttling position so as to reduce the rate of supply of fluid under pressure to said cylinder during initial movement of said contact means from the open circuit position, and means operative to release said latch after said piston has been moved through a predetermined portion of a stroke in closing said contact means to cause said valve means to be moved to open position.

8. A fluid pressure operated circuit breaker r aving contact means moving to open circuit osition and to closed circuit position, an operating cylinder, a piston operative upon supply of fluid under pressure to said cylinder for moving said contact means to closed circuit position, spring means operative to move said contact means to open circuit position, fluid pressure control means including a passage for supplying fluid under pressure to said cylinder, a valve biased toward an open position and movable to a throttling position to control the flow of flu d under pressure through said passage, a positive latch operative to hold said valve in throttling position, and lever means cooperative with said piston and connected to said valve for shifting it to the throttling position to reduce the rate of flow of fluid under pressure to said cylinder during initial movement of said contact means from the closed circuit position, a lost-motion connection between parts of said lever means so that the part thereof connected to said valve may remain stationary while the other part thereof moves said latch to released position.

9. In a fluid pressure operative circuit breaker of the type including movable contact means, means for moving said contact means to an open circuit position, a movable abutment operative upon an increase in the pressure of fluid in a chamber for moving said contact means to a closed circuit position, and supply valve means operative to supply fluid under pressure to said chamber, the combination therewith of throttle valve means interposed between said supply valve means and said chamber, said throttle valve means comprising a spring, a valve element biased by said spring toward an open position for permitting supply of fluid to said chamber at a maximum rate, a latch for releasably holding said throttle valve means in a throttling position to reduce the rate at which fluid under pressure can be supplied to said chamber, lever means having a lost-motion operative relative to said movable abutment for permitting retention of said valve element in the throttling position only when said abutment is shifted to a position corresponding to the open circuit position of the contact means, said lever means having a second lost-motion connection therein so as to be operative to release said latch upon a predetermined movement of said abutment for closing said contact means.

10. In a fluid pressure operated circuit breaker having relatively movable contact means, a cylinder, and a piston operative upon an increase in fluid pressure in said cylinder for moving said contact means, the combination of supply valve means operative to supply fluid under pressure through a communication to said cylinder, throttle valve means interposed in said communication having a position for restricting flow there- REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,379,178 Peek June 26, 1945 2,381,307 Peek et a1. Aug. 7, 1945 2,384,801 Cumming et al Sept. 18, 1945 1,641,131 Baker Aug. 30, 1927 1,714,545 Burns May 28, 1929 

